Forgot to add, I tied a small loop of rope around the handle of the velux window to latch onto when I am reaching up with the boathook. A quick tug allows me to open the vent, or open the window fully. Pushing on the boathook closes the window.
It doesn't look pretty, but my window is up a tunnel in the flat ceilinged hallway, so it's not obvious. No doubt a better looking loop of something could be found, if that's the road they go down.